1. Field of the Invention
This invention relates to a method and apparatus for controlling a rotating biological contactor in which the rate of weight change is monitored to determine the presence of conditions adverse to the maintenance of biological growth on the contactor.
2. Description of the Prior Art
In biochemical reactions, such as the treatment of waste water, it is known in the art to measure changes in various conditions and to alter treatment of the reaction in response to such changes. Thus, for example, in U.S. Pat. No. 3,684,202, activated sludge is recycled to main sewage aerating tanks based on the measurement of the biological oxygen demand (BOD) of the sewage whereas in U.S. Pat. No. 4,130,481, the recycle is determined by sludge density and CO.sub.2 production.
In U.S. Pat. No. 4,183,810, the BOD supply to a final denitrification step is controlled by analysis of the nitrite-plus-nitrate content in the process liquid.
In U.S. Pat. No. 4,276,174, the temperature of an aerated mixture of sludge is sensed and the rate of introducing oxygen-containing gas into the mixture is controlled in response thereto.
In U.S. Pat. No. 4,277,342, sludge influent is treated in an aerated mixing tank wherein the pH and the oxidation reduction potential or dissolved oxygen content is measured and acid and oxygen is respectively supplied in response to the measured levels.
In German Offenlegungsschrift No. 2532199, the activity of microorganisms in a sewage treatment plant is supervised and controlled by the measured oxygen demand at the measured temperature, oxygen concentration and turbidity level. In this system, pH values are kept constant by the metered addition of acid or alkaline solution.
One means of treating waste water is through the use of rotating biological contactors wherein biological slimes on the contactors aerobically digest the organic content in the waste water. Various arrangements incorporating rotating biological contactors are described in U.S. Pat. Nos. 3,484,836, 3,704,783 and 4,130,482. Additionally, U.S. Pat. No. 3,516,929, the inlet for the waste water flow to a plurality of rotating contactors is opened or closed according to the liquid level sensed by probes in the channel in which the contactors are located.
The use of rotating biological contactors provides an efficient and effective manner of treating waste water. Unfortunately, it has been found that the biological slime on the contactors is sensitive to toxic materials whereby the presence of toxic materials in the waste water may destroy the biological slime and render the rotating biological contactors useless for their intended purpose. Conventional sensing devices, such as those described previously, generally are not capable of determining an increase of those toxic materials which will adversely affect the biological slime. Moreover, even if sensing devices for the toxic materials could be developed, the necessary level of sensitivity would by difficult to achieve. In this regard, the constant contact with the waste water would tend to corrode or foul the sensing device thereby preventing its operation or affecting its sensitivity.